It isn't a part from an Erma .22 conversion kit.
To me, it appears to be an adjustable rear sight base. The depression would hold the end of a coil spring, and the thing would pivot on a pin through the 2 "ears." But this does not solve the mystery of what gun it would belong on.
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"... Liberty is the seed and soil, the air and light, the dew and rain of progress, love and joy."-- Robert Greene Ingersoll 1894
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